In modern society, elevators have become ubiquitous machines for transporting people and cargo through buildings of multiple stories. Upon their advent, cities immediately had the option of building upwardly as opposed to only outwardly, thereby contributing to the modern high-rise city landscape and current urban planning models.
Today, the levels of the highest buildings in the world continue to grow, with buildings over one-hundred stories being commonplace; the limits for skyscrapers are being pushed to one hundred and fifty floors or more. That increased height creates multiple new challenges and magnifies existing ones for elevator designers. For example, in a building of such height, is not uncommon for the building at its apex to sway back and forth in excess of three feet or more. Accordingly, each of the mechanical components of the building, including the elevator, must be built to withstand such lateral motion. This is particularly true in areas prone to high winds or earthquakes, where building sway could be even more severe.
One challenge created by the sway of very high buildings has been to provide a mechanism by which the derailment of the elevator car, counterweight, or other moving component can be easily detected with minimal false readings. For years, such detection systems have primarily consisted of a so-called “ring and string” device wherein an electric conductor such as a wire string is extended vertically through the hoistway of the elevator and held at electrical potential. The string is typically mounted only at the top and bottom of the hoistway. A sensing ring is in turn physically mounted to a movable element in the hoistway, such as the counterweight. The sensing ring completely circumscribes the electrical conductor but in spaced relation thereto. When installed and properly aligned, as the counterweight moves up and down on the rail, the sensing ring does not come in contact with the electrical conductor, even with a moderate level of building sway. However, if the counterweight becomes derailed, the sensing ring will contact the electrical conductor. Because the conductor is held at potential, the contact between the ring and the conductor closes a circuit, directing current to flow from the conductor into the counterweight, which in turn is detected by the derailment detection system of the elevator.
As building heights have steadily increased, the sway component mentioned above tends to cause more false readings in the derailment detection system than is desired by the end-user. In particular, even when the counterweight or the movable element within the hoistway are properly mounted on the rails of the system, if the building encounters significant sway either due to high winds or otherwise, the rails on which the movable element is mounted will tend to sway with the building, and in turn cause the sensor itself to sway. However, the electrical conductor stays fixed within the hoistway, in which it is attached only at its top and bottom, so that when the rail and counterweight sway, the ring can potentially contact the wire or electrical conductor, resulting in improper activation of the elevator derailment detection system. This not only inconveniences the end-user in that the elevator will stop or otherwise become less than fully operational, but also results in added expense in terms of maintenance costs for the building.